Coating compositions and bulk resins derived from epoxy/isocyanate crosslinking are known in the art as shown by Senger, J. S.; Yilgor, I.; McGrath, J. E.; Patsiga, R. A. (J. Appl. Polym. Sci., 1989, 38(2), 373-82); Fujiwara, Masahiro; Baba, Akio; Matsuda, Haruo (J. Heterocycl. Chem., 1988, 25(5), 1351-7); Marks, Maurice J. (Polym. Mater. Sci. Eng., 1988, 58, 864-8); Uribe, M.; Hodd, K. A. (Polym. Prepr. (Am. Chem. Soc., Div. Polym. Chem.), 1984, 25(2), 43-4); Kordomenos, P. I.; Frisch, K. C.; Kresta, J. E. (J. Coat. Technol., 1983, 55(700), 59-61); U.S. Pat. No. 4,066,628 filed Aug. 2, 1976; Ashida, K. (Eur. J. Cell. Plast., 1980, 35 3(4), 122-5); Hefner, Robert E., Jr. U.S. Pat. No. 4742146, 1988); Mueller, Hanns Peter; Kerimis, Dimitrios; Heine, Heinrich; Uerdingen, Walter (Ger. Offen., DE 3600764, 1987); and Kaneko, Shoroku; Yamaoka, Sigenori; Mizuno, Masuo; Okabe, Yukihiro (Fr. Demande, FR 2499579, 1982). In almost all these cases elevated temperatures are necessary to affect the condensation reaction between isocyanate and epoxy functionalities. An ambient temperature condensation reaction between isocyanates and epoxides has been developed by Trost, Barry M.; Sudhakar, and Anantha R. (J. Am. Chem. Soc., 1988, 110(23), 7933-5) but requires the use of an expensive palladium catalyst and the epoxy group must be a vinyl substituted epoxy. These restrictions severely limit the utility of this method. None of the above citations disclose or suggest the use 1,3-disubstituted imidazole-2-thiones to catalyze the condensation reaction between epoxy and isocyanate functionality.
Unrelated references such as Berstein, P. (U.S. Pat. No. 3,708,344 1973); Martin, S. (U.S. Pat. No. 4,176,017 1979); Yee, G. (U.S. Pat. No. 3,841,982 1974) disclose the use of 1,3-disubstituted imidazole-2-thiones as depolarizers and modifiers for electrochemical deposition. These citations do not disclose or suggest use 1,3-disubstituted imidazole-2-thiones to catalyze the condensation reaction between epoxy and isocyanate functionality. Several preparations have been reported for 1,3-disubstituted imidazole-2-thiones such as Benac, B; Burgess, E. M.; Arduengo, A. J., III (Organic Syntheses, 1986, 64, 92), however these preparations do not teach or suggest the utility of 1,3-disubstituted imidazole-2-thiones as crosslinking agents for epoxy/isocyanate systems. The use of 1,3-disubstituted imidazole-2-thiones as crosslinking agents for epoxy/anhydride reactions is disclosed in commonly assigned, co-pending cases Ser. No. 07/389,897 and Ser. No. 07/389,895 which were both filed on Aug. 4, 1989.